68 GEOLOGY OF ERIE COUNTY 



Effects of Glaciation. 



The action of the glacier upon the land which it overrode 

 may be classified as follows : 



Erosion by ice. 



Deposition by ice. 



Erosion by streams fed by glacial waters. 



Deposition by these streams. 



Erosion by the waves of lakes held in by the glacier. 



Deposition in or by glacial lakes. 



Erosion by the Glacier. 



The tremendously heavy mass of ice dragging slowly over 

 the surface of the land acted upon the land beneath exactly like 

 a plane. Imbedded in its bottom were rocks, pebbles and sand 

 which, as they were dragged along a land surface, scored, 

 scratched and polished hard rocks and deeply eroded the softer 

 shales. Where the motion was at right angles to slopes the ice 

 tore away the northward fronting slope, but rode smoothly down 

 the southward slope with little erosion. When the movement was 

 parallel to the slopes, as in the valleys of north and south 

 streams, the glacier may have widened and deepened them, by 

 erosion at the bottom and sides. 



In Erie county the erosion by the ice is plainly shown on 

 the surfaces of outcrops of Onondaga limestone. Wherever fiat 

 exposures of this are exposed by streams or excavations the 

 surfaces are found to be planed smooth or scored deeply with 

 parallel striae, the work of the sand and gravel imbedded in the 

 glacier. 



Transportation and Deposition by the Glacier. 



The detritus derived from the scouring action of the ice 

 upon the surface underlying it was transported sometimes to 

 long distances. Much of it was deposited as moraines along the 

 ice front. Some was deposited under the ice as drumlins. 



It is this deposition of detritus that so materially changed 

 the topography of the county. The soil of all the county is 

 primarily the result of this deposition and transported detritus 

 has been left behind in such enormous quantities as to bury or 



